The invention is in the field of packing technology and relates to a closure unit for a container for a flowable product, as well as to a production process for said closure unit and a coated cardboard container with a corresponding closure unit.
Containers for flowable products require an opening or a potential opening through which the product can be removed. It is advantageous if, following the first opening, said opening can be resealed, because only then is it possible to handle the container following the first removal of product in the same way as before this has taken place. Therefore most such containers are provided with a closure unit, which can have the most varied forms and shapes and which can be made from the most varied materials. Known examples for such closure units are stoppers made from cork and other materials, screw closures made from plastic or metal, clip or tack closures with ceramic plugs and rubber seals, ground glass stoppers, snap closures made from plastic, etc. Following the initial opening a container without a closure cannot be tightly sealed again. The latter e.g. include glass ampules, many beverage containers made from metal, coated cardboard or plastic.
In the case of containers having a neck, closure units mainly only consist of a closure part, which is mounted on the neck (container closed) or is not located thereon (container open), i.e. which can form a reversible, tight connection with the container. In the case of containers without a neck the closure unit mainly consists of a pouring part (or neck part) and a closure part, the pouring part being connected in a substantially irreversible, tight manner to the container, whereas the closure part and the pouring part together form a reversible, tight connection. In all cases the function of the closure unit is the closing of an opening or potential opening in the container in such a way that the opening can be opened by simple manipulations and then resealed. The closure unit is so designed that between the closure part and the container (closure unit without pouring part) or between the closure part and the pouring part (closure unit with pouring part and closure part) a tight connection can be formed and then removed again with simple manipulations.
The tight sealing of the container is the main function of the closure unit and substantially determines the design and material thereof. However, in many cases the closure unit must also fulfil other functions. These are e.g. in the case of large openings a minimum mechanical support function, in the case of a wine bottle cork a minimum gas permeability, for ease of handling e.g. a permanent connection between the container and the closure part, for safety reasons means which render visible from the outside an initial opening and so on. For the case of a closure unit having a closure part and a pouring part, the most important additional function, apart from the in this case irreversible, tight connection to the container, is the reversible seal between the two parts.
Such a multifunctionality of the closure unit makes obvious such a unit made from several materials, because then for each function it is possible to use an optimum, suitable material.
Numerous closure units made from several materials are known, e.g. a screw cap with a sealing insert (functions: stability/positive engagement, sealing), a cork stopper with a tin cap (functions: sealing, making visible the first opening), a clip closure with a metal clip, the ceramic plug and the rubber seal (functions: connection of the container neck and closure part also in the opened state, mechanical stability and sealing). The disadvantage of all these closure units compared with those made from a single material is that manufacture is made more complicated. Each individual part must be separately manufactured, then the individual parts must be assembled and fixed as a unit to the container, or the individual parts must be fitted to the container in separate steps.
Similar disadvantages and numerous desired improvements, which are detailed hereinafter, also occur in the case of closure units formed from a pouring part and a closure part, particularly those closure units, such as correspond to the prior art coated cardboard containers for beverages.
Containers made from coated cardboard for flowable products are in particular widely used in the food industry to contain drinks or beverages. There are essentially two different types. They are either produced as a quasi-continuous tube, then filled in one operation, sealed at both sides and then brought into an e.g. rectangular shape by folding down the corners. Containers produced in this way are completely filled with liquid. Prior to opening, by folding up at least one corner it is necessary to produce a slight vacuum, so that the container can be opened by tearing off a corner region without overflowing. The folded up corner then serves simultaneously as a spout. It is also possible to produce the cardboard container empty and open at one end, which is then filled and is then closed at said open end by folding and welding. Such containers are not entirely filled with liquid. On such containers conventionally a spout is formed by folding up and at this point the container is opened by tearing. The tearing open of the cardboard container is irreversible. Once the container has been opened, it cannot be resealed, which limits the use thereof.
In order to obtain less use-limited cardboard containers of this type, various closure units made from different materials have been created with the aid of which the container can be resealed following the initial opening. Such closure units are fitted to the containers prior to filling and namely in the closed state, because they do not have to serve as filling openings. In order that such a closure unit effectively improves the container and extends the possible uses thereof, but does not unacceptably increase its price, a number of different requirements are made. The following list gives the most important requirements roughly in priority order:
The closure unit must be manufacturable from materials, which are suitable for contact with foods, ecologically unobjectionable and inexpensive.
The closure unit must be inexpensive to manufacture and fit to the container, i.e. the minimum number of operations should be involved in the manufacture and fitting, with ideally a single manufacturing step and a single fitting step.
The closure unit must have a closure part, which can be opened a random number of times and also resealed tightly.
The closure unit must have a pouring part, so that the cardboard container does not have to be folded up for forming a spout.
The closure unit must be such that the container, particularly prior to the initial opening, is able to withstand without damage rough transportation.
The closure unit must be openable without undue force and with simple manipulations, including the first opening.
The closure unit must be hygienic to handle, i.e. its normal handling should not involve any engagement in the pouring opening.
The closure unit must be connected as a whole to the container so as to allow easy handling for any normal container use, i.e. there must be no waste parts at the initial opening and the closure part must be permanently fixed to the pouring part, but at the same time not impede pouring.
The closure unit must be manufacturable in a large number of different variants from the shape and colour standpoints, which satisfy high esthetic demands.
Numerous closure units for such uses are known, which are fitted or fittable to internally coated cardboard containers. Some of these will now briefly be described and compared with an ideal closure unit with respect to the above list of requirements.
Such a closure unit e.g. comprises a pouring part and a screw or snap top, which in the new state are interconnected by a tear or rupture ring, all the parts being made from a thermoplastic material. The pouring part and the top, onto which the tear ring is shaped with a predetermined breaking point, are individually manufactured, fitted to one another, the tear ring and pouring part are welded together and are then fitted to the container mainly by welding to the inner coating and it must be possible to carry out the welding to the container and of the tear ring and pouring part in a single operating step. Measured against the above requirements list this closure unit suffers from the disadvantage that its manufacture and fitting requires an excessive number of working steps, particularly if for hygienic reasons following the assembly of the two parts a cleaning stage is required. In addition, the tear ring constitutes a waste part, which exists following the initial opening. On opening the screw or snap top must be completely removed from the pouring part and is then lost. The screw top must always be circular, the snap top is advantageously circular, so that there are very limited shape possibilities with respect thereto.
Roughly the same disadvantages are encountered in the case of closure units, which within the pouring part have a sealing diaphragm, which must be removed at the initial opening. Such a diaphragm serves as an additional seal prior to the initial opening. Such a diaphragm can usually only be removed by introducing the fingers into the pouring opening, which does not satisfy the requirement of hygienic handling.
Other closure units with sealing diaphragms in the pouring opening are provided with perforating or puncturing parts, which must be introduced through the diaphragm either manually (hygiene!) or automatically on the initial unscrewing of the screw top. Such closure units are only manufacturable in a large number of steps, but can have as the additional advantage in the puncturing part a venting channel, which permits uninterrupted pouring even when the spout is relatively narrow.
Closure units with snap tops can be moulded in one piece, the pouring part (with or without an additional sealing diaphragm) being connected by means of a connecting part, said connecting part also serving as a permanent connection between the two parts. Although such closure units fulfil the requirement of one-step manufacture, they must be closed following the latter, which means a further production step. This can be obviated in that a diaphragm is moulded in the pouring part and which has an adequate stability to provide an adequately stable closure for the container prior to the initial opening. In such a case the container can be made commercially available with an "opened" closure unit. If such closure units are compared with the requirements list, it can be seen that although manufacture is possible in one step, it requires extremely complicated moulds and the design of the top is very limited from the material standpoint, although only to a much lesser extent from the shape standpoint. The material of the entire closure unit must be easily tightly connectable, e.g. by welding to the container and normally to the coating and is consequently defined within narrow limits. As the cardboard container is usually coated with polyethylene, the complete closure unit is also made from polyethylene and can consequently not satisfy higher esthetic requirements.
Much the same applies with regards to closure units which largely comprise a closing diaphragm, which is initially opened along a predetermined breaking point and on which a sealing lip is shaped in such a way that it can fulfil the sealing function on reclosing. Such closure units can be manufactured very inexpensively, but in the new state are made sensitive by the exposed predetermined breaking point. These closure units can also not satisfy high esthetic demands. Such a closure unit can also not ensure adequate sealing following initial opening.
Clearly none of the above-described closure units satisfies the complete list of requirements.